1. Field of the Invention
The present invention relates to an air-intake structure of an internal combustion engine.
2. Description of Background Art
An internal combustion engine having a structure is known wherein air-intake valves reciprocate in parallel with the reciprocal motion of pistons, and cams of a camshaft directly press the air-intake valves. See, for example, JP-B-1-16983.
Since the internal combustion engine described above has a structure in which the direction of the reciprocal motion of the pistons is in parallel with the air-intake valves, the opening planes of air-intake ports opening into a combustion chamber are parallel to the mating surface of a cylinder head with respect to a cylinder block, and the air-intake ports are bent from the opening planes and extend obliquely upwardly, and extend further outwardly from the side wall of the cylinder head.
The air-intake ports disclosed in JP-B-1-16983 project outwardly from the side wall of the cylinder head and extend upwardly up to the mating surface of the cylinder head with respect to a cylinder head cover, and then are connected to air-intake pipes (intake manifolds), and the air-intake pipes extend so as to curve across the portion above the cylinder head cover.
Fuel injection nozzles are provided on the air-intake pipes.
Since the air-intake ports projecting outwardly from the cylinder head swell outwardly and extend upwardly to the mating surface of the cylinder head with respect to the cylinder head cover, the air-intake ports protrude significantly outwardly of the cylinder head, so that the cylinder head is upsized.